1. Field of the Invention
The invention is directed to a friction clutch to be arranged in the power train of a motor vehicle.
2. Description of the Prior Art
A conventional friction clutch to be arranged in the power train of a motor vehicle includes a flywheel which is rotatable about an axis of rotation. The flywheel can be coupled to one end of a crankshaft of an internal combustion engine and has a friction surface facing away axially from the crankshaft. A friction facing of a clutch disk connectable with a transmission input shaft is connected in a frictional engagement with the friction surface of the flywheel when the friction clutch is engaged. A pressure plate unit is provided in order to apply the contact pressure force needed for the frictional engagement between the friction facing of the clutch disk and the friction surface of the flywheel. The pressure plate unit comprises a clutch housing which is rigidly connected with the flywheel radially outside the friction facing and extends radially inward so as to partially surround the clutch disk. A contact-pressure plate is supported axially against the clutch housing via a clutch spring. The contact-pressure plate is provided with a friction surface which is located opposite the friction surface of the flywheel facing the crankshaft and communicates with a friction facing of the clutch disk in a frictional connection when the friction clutch is engaged. Frictional forces of roughly equal magnitudes are transmitted to the clutch disk by the friction surface of the contact-pressure plate and the friction surface of the flywheel given an identical construction of these two friction surfaces. Torque is accordingly transmitted from the crankshaft to the clutch disk connected with the transmission input shaft via two separate torque transmission paths. The first torque transmission path extends from the flywheel, via the friction surface of the flywheel, directly to the clutch disk. The second torque transmission path extends from the flywheel to the clutch disk via the clutch housing, clutch spring, contact-pressure plate and friction surface provided at the latter. Torques of approximately equal magnitude are transmitted via both torque transmission paths.
In addition to the torques to be transmitted by the friction clutch during normal driving and shifting operation, peak torques which are generated, for example, by incorrect operation such as engaging the clutch in a jerking manner, are also transmitted to the clutch disk by the frictional engagement between the flywheel and clutch disk. In this connection, there exists the risk that these peak torques can damage components of the friction clutch itself, as well as components of the gearbox or transmission. In order to withstand these peak torques, which only occur occasionally, these components must exhibit a mechanical strength and robustness beyond that required for normal operation.